I'm not so sure this is an oxymoron. Something can be close to being exact, if not for a slight difference (e.g. if it were September 1st when it was released), it's not quite exactly 25 years, but it almost is. If you were to say just 'Almost 25 years ago' then that could really be any number of years around 25 (24 years, 26 years) rather than having it down to the exact day/month.